Method of manufacturing a display device

ABSTRACT

ICs ( 20 ) are nearly separated from the semiconductor substrate ( 10 ) on/in which they are formed. Subsequently, the substrate is positioned upside down on a substrate (carrier) ( 3 ) which is provided with glue ( 21 ) at the location of a crystal. After attachment of the crystal to the carrier, the semiconductor substrate is removed and the crystal remains attached to the carrier e.g. at the crossing of rows and columns. The separate crystals may contain TFTs (simple AM addressing) but also more complicated electronics (address of pixel in memory+identification).

[0001] The invention relates to a method of manufacturing a displaydevice, in which a substrate is provided with groups of at least onepixel and a conductor pattern, and in which a semiconductor device forsupplying drive voltages to the pixel is fixed to the substrate.

[0002] Examples of such active matrix display devices are the TFT-LCDsor AM-LCDs which are used in laptop computers and in organizers, butthey also find an increasingly wider application in GSM telephones.Instead of LCDs, for example, (polymer) LED display devices can be used.

[0003] More generally, the invention relates to a method ofmanufacturing an electronic device, in which at least a substrate isprovided with functional groups comprising at least a switching element,and in which a semiconductor device for supplying drive voltages to theswitching element is fixed to the substrate.

[0004] The article “Flexible Displays with Fully IntegratedElectronics”, SID Int. Display Conf., September 2000, pp. 415 to 418,describes a process in which specifically formed semiconductor devicesin a liquid suspension are passed across a substrate and reachcorrespondingly formed “apertures” or indentations in the substrate. Thesemiconductor devices are ICs which are manufactured by means ofstandard techniques. After the ICs have been provided, connections withpixels are established.

[0005] A problem occurring in this case is the fact that, for providingthe ICs, considerable tolerances are to be taken into account. Not onlymust the semiconductor devices (ICs) glide, as it were, into theindentations but they also have a certain thickness (approximately 50micrometers). Dependent on variations of thickness, certainly when notall ICs come from one and the same wafer, and variations on the surfaceof the substrate in the depth of the “apertures” or indentations, avariation will occur in the thickness of the electro-optical layerprovided on the substrate, which thickness may amount to severalmicrometers. Notably when thickness-sensitive effects such as, forexample, the (S)TN effect are used, this leads to unwanted discolorationand non-uniform switching behavior.

[0006] Inaccuracies during placement of the ICs must also be taken intoaccount. When an IC “glides into the indentations”, it may find itsultimate destination at an arbitrary location within the indentation.Consequently, the indentations occupy a much larger space than thesemiconductor devices (ICs), which, notably in transparent displaydevices, is at the expense of the aperture. To be able to satisfactorilycontact the ICs in the case of this inaccurate placement, these ICs mustbe provided with large contact surfaces, which is at the expense of ICsurface area and renders the technology shown very expensive.

[0007] A further problem is the variation of the thickness of thesemiconductor devices (ICs), related to the depth variation of theindentations so that local thickness variations occur in the ultimatesurface area (the common surface area of the substrate). Conductortracks extending in the device shown across the embedded semiconductordevices (ICs), thereby run a great risk of breakage.

[0008] To this end, a semiconductor substrate according to the inventionis provided with a plurality of semiconductor devices whose surfaceshave electric connection contacts, the semiconductor devices beingmutually separated in a surface region of the semiconductor substrateand the electric connection contacts being coupled to the conductorpattern (in an electrically conducting manner) whereafter thesemiconductor devices are separated from the semiconductor substrate.

[0009] Since the semiconductor devices (ICs) are similarly situated withrespect to each other as on the semiconductor substrate during theirfixation to the substrate, the ICs are provided at a very accuratepitch. This may be a constant pitch in one direction, such as inmatrix-shaped configurations of the pixels. The pitch may alternativelybe variable.

[0010] Moreover, due to this method of fixation, only parts of thesurface area of the semiconductor substrate in which the active elementsare realized can be provided on the substrate of the display device.Since these parts have a negligible thickness (less than 1 micrometer),said thickness-sensitive effects do not occur. Even the presence of aspacer at the location of an IC does not have any influence or hardlyhas any influence on the effective thickness of the liquid layer andhence on the operation of the display device, certainly when spacerswith an elastic envelope are chosen.

[0011] A further advantage is that the ICs can now comprise driveelectronics at the location of the pixels. This provides great freedomof design.

[0012] The semiconductor devices are separated, for example, by means ofan etching treatment in a surface area of the semiconductor substrate.In an alternative method, the semiconductor devices are provided in asemiconductor layer on an insulating layer (SOI technology) andseparated by means of an etching treatment in this semiconductor layerhaving a thickness of typically 0.2 micrometer. The result is that thesesemiconductor devices in the finished display device have a negligiblethickness (less than 1 micrometer) as compared with the effectivethickness of the liquid layer, so that said thickness-sensitive effectsdo not occur, not even in the presence of a spacer at the location of anIC. Moreover, the ICs are now placed with great accuracy and withouttaking extra precautions. The contact surfaces may now be considerablysmaller, which occupies less IC surface.

[0013] These and other aspects of the invention are apparent from andwill be elucidated with reference to the embodiments describedhereinafter.

[0014] In the drawings:

[0015]FIG. 1 is a diagrammatic cross-section of a part of a displaydevice according to the invention,

[0016]FIG. 2 shows diagrammatically a flow chart of the method,

[0017]FIGS. 3 and 4 show diagrammatically steps during the manufactureof the display device of FIG. 1,

[0018]FIGS. 5 and 6 show diagrammatically the semiconductor substrateand the substrate of the display device during manufacture of thedisplay device of FIG. 1, while FIG. 7 is an electrical equivalent of apossible embodiment of a display device according to the invention, and

[0019]FIG. 8 shows an electron-microscopic image of the semiconductorsubstrate for fixation of the display device to the substrate.

[0020] The Figures are diagrammatic and not drawn to scale.Corresponding elements are generally denoted by the same referencenumerals.

[0021]FIG. 1 is a diagrammatic cross-section of a part of alight-modulating cell 1 with a liquid crystal material 2 which ispresent between two substrates 3, 4 of, for example, glass or syntheticmaterial, provided with (ITO or metal) electrodes 5, 6. Together with anintermediate electro-optical layer, parts of the electrode patternsdefine pixels. If necessary, the display device comprises orientationlayers (not shown) which orient the liquid crystal material on the innerwalls of the substrates. The liquid crystal material may be a (twisted)nematic material having, for example, a positive optical anisotropy anda positive dielectric anisotropy, but may also make use of the STNeffect, a bistable effect, a chiral nematic effect, or the PDLC effect.The substrates 3, 4 are customarily spaced apart by spacers 7, while thecell is sealed with a sealing rim 8 which is customarily provided with afilling aperture. A typical thickness of the layer of liquid crystalmaterial 2 is, for example, 5 micrometers. The electrodes 5, 5′ have atypical thickness of 0.2 micrometer, while also the thickness of thesemiconductor devices (ICs) 20 is about 0.2 micrometer in this example.In FIG. 1, a spacer 7 is shown at the location of an electrode 5′ and IC20. The overall thickness of electrode and IC 20 is substantiallynegligible as compared with the thickness of the layer of liquid crystalmaterial 2. The presence of the spacer 7 does not have any influence, orhardly has any influence, on the opto-electrical properties of thedisplay device, notably when spacers with a hard core 8 and an elasticenvelope 9 having a thickness of about 0.2 micrometer are chosen.

[0022] For manufacturing the semiconductor devices (transistors or ICs)20, use is made of conventional techniques. The starting material is asemiconductor wafer 10 (see FIG. 2, step I^(a), FIG. 3), preferablysilicon, with a p-type substrate 11 on which an n-type epitaxial layer15 having a weak doping (10¹⁴ atoms/cm³) is grown. Prior to this step, amore heavily doped n-type layer 13 (doping about 10¹⁷ atoms/cm³) isprovided by means of epitaxial growth or diffusion. Further processsteps (implantation, diffusion, etc.) realize transistors, electroniccircuits or other functional units in the epitaxial layer 15. Aftercompletion, the surface in the example of FIG. 3A is coated with aninsulating layer such as silicon oxide. Contact metallizations 17 areprovided via contact apertures in the insulating layer by means oftechniques which are customary in the semiconductor technology. Ann-type region 14 (doping about 10¹⁷ atoms/cm³) is provided between thetransistors, electronic circuits (ICs) or other functional units,likewise by masked doping (before or after providing the insulatinglayer 16).

[0023]FIG. 3B shows a variant of FIG. 3A, in which the transistors,electronic circuits or other functional units are realized in the SOItechnology in which the thin surface area 15 is embedded in insulatinglayer 19. In the example of FIG. 3B, the contact metallizations 17 aredirectly provided on contact regions of the transistors of thesemiconductor devices.

[0024] Subsequently, the n-type regions 14 are subjected via a mask toan etching treatment with HF (under the influence of an electric field).In this treatment, the heavily doped n-type region 14 is isotropicallyetched, as well as the underlying n-type epitaxial layer 13. The weaklydoped n-type epitaxial layer 15 is, however, etched anisotropically sothat, after a given period, only a small region 25 remains in this layer(see FIG. 2, step I^(b) FIG. 3).

[0025] The transistors, electronic circuits (ICs) or other functionalunits are, however, still at their originally defined position. Aregular pattern of such units will generally be manufactured at a fixedpitch.

[0026] Prior to, simultaneously with or after this treatment, substrates3 of the display device are provided with metallization patterns which(also at defined positions) will comprise one or more electrodes 5′(FIG. 2, steps II^(a), II^(b)). In this example, the parts 5′ of themetallization patterns on the substrate 3 are ordered similarly (thesame pitch in different directions) as the electronic circuits (ICs) 20in the semiconductor wafer 10.

[0027] In a subsequent step, the semiconductor wafer 10 is turned upsidedown, in which the metallization patterns 5′ on the substrate 3 areaccurately aligned with respect to the electronic circuits (ICs) 20 inthe semiconductor wafer 10 (FIG. 4), whereafter electrical contact isrealized between metallization patterns 5′ and the contactmetallizations 17. To this end, use is made of, for example, aconducting glue 21 or anisotropically conducting contacts on theelectrodes 5′. The electronic circuits (ICs) 20 are detached from thesemiconductor wafer 10 by means of vibration or by a different method.The substrate 3 is then obtained which is provided with pictureelectrodes 5 and ICs 20 which are very accurately aligned both withrespect to the picture electrodes 5 and with respect to each other (stepIII in FIG. 2). Moreover, the reduction of aperture is exclusivelydetermined by the dimension of the ICs (or transistors).

[0028] Also when using SOI technology, a first separation between thevarious electronic circuits (ICs) 20 can be made by means of a HFetching treatment or other methods which are conventional in thesemiconductor technology, which ICs are subsequently detached from thesubstrate also by means of vibration or by means of another method.

[0029] Not all ICs (transistors) of the substrate 10 are detached fromthe substrate during this step, because the pitch pa of themetallization patterns 5′ is usually much larger than the pitch p₁ andpitch p₂ of the ICs 20. This will be further explained with reference toFIG. 5. If the substrate 3 has a size of the order of (or smaller than)the region indicated by the block 22 of detachable ICs, only the ICs 23(black ICs in FIG. 5) are detached and provided on the substrate.

[0030] If the substrate 3 is larger than the diagrammatically shownblock 22 of detachable ICs, the ICs 23 (black ICs in FIG. 5) are firstdetached and provided on the part 26 on the substrate 10 (see FIG. 6).Subsequently the adjacent ICs 24 (see FIG. 5) are detached and providedon the part 27 of the substrate 10. Similarly, ICs 20 are provided onthe parts 28, 29.

[0031] The display device 1 is subsequently completed in a customarymanner, if necessary, by providing orientation layers which orient theliquid crystal material on the inner walls of the substrate. Spacers 7are customarily provided between the substrates 3, 5, as well as asealing rim 8 which is customarily provided with a filling aperture,whereafter the device is filled with LC material in this example (stepIV in FIG. 2).

[0032] Since the semiconductor devices (ICs) 20 are made in advance,more extensive electronic functions can be realized therein than in theconventional polysilicon technology. Notably when using monocrystallinesilicon, it is possible to realize functions with which a different typeof architecture of the display device can be made possible than with theconventional matrix structure. Such a device 30 is shown in FIG. 7,which is a device having a bus structure. The ICs (semiconductordevices) 20 are connected to a supply voltage via connection lines 31,32 (in this example, line 31 is connected to earth), while the lines 33,34 supply information and, for example, a clock signal. Since, asdescribed above, the location of an IC to be provided is known inadvance, this may be provided first (during IC processing or via e-PROMtechniques), for example, with an address register and one or more dataregisters. For certain ICs (and associated (groups) of pixels 35), theaddress is recognized by the ICs and picture information is stored,whereafter it is applied to the pixels 35, dependent on commands to bealso supplied through the lines 33, 34.

[0033]FIG. 8 is an electron-microscopical image of the semiconductorsubstrate for fixation to the substrate (FIG. 2, step I^(b)).

[0034] The protective scope of the invention is not limited to theembodiment described. As stated in the opening paragraph, the pixels mayalso be formed by (polymer) LEDs which may be provided separately or asone assembly, while the invention is also applicable to other displaydevices, for example, plasma displays, foil displays and display devicesbased on field emission, electro-optical or electromechanical effects(switchable mirrors). Where the examples state a pitch in an orthogonalsystem of co-ordinates, the localization may also take place in a radialsystem of co-ordinates or in a tree structure (fractal structure). Asalready stated, the pitch may also be variable. This provides thepossibility of manufacturing, for example, circular or elliptic displaydevices.

[0035] The examples stated the direct electric contact of the ICs onmetallization patterns 5′ that were already present. Since the detachedICs have a small thickness, they may also be provided directly on thesubstrate 3, in which method apertures which are metallized are etchedthrough the layers 15 by means of an etching method. The contactmetallizations then extend across the ICs and make contact (for example,via contact apertures in an insulating layer) with through-metallizedconnections to the contact metallizations 17.

[0036] Said contacts do not need to be electrically conducting contacts.In given applications, it may be useful to provide a capacitive couplingbetween the contact metallizations 17 and the metallization patterns 5′,for example, by providing one or both with a thin insulating layer.

[0037] As also stated in the opening paragraph, the method is notlimited to display devices. The invention is notably applicable toelectronic devices (sensors) in which the substrate is provided withfunctional groups.

[0038] Alternatively, as stated, flexible substrates (syntheticmaterial) may be used (wearable displays, wearable electronics).

[0039] The invention resides in each and every novel characteristicfeature and each and every combination of characteristic features.Reference numerals in the claims do not limit their protective scope.Use of the verb “to comprise” and its conjugations does not exclude thepresence of elements other than those stated in the claims. Use of thearticle “a” or “an” preceding an element does not exclude the presenceof a plurality of such elements.

1. A method of manufacturing a display device, in which a substrate isprovided with groups of at least one pixel and a conductor pattern andin which a semiconductor device for supplying drive voltages to thepixel is fixed to the substrate, the method comprising the steps ofproviding a semiconductor substrate with a plurality of semiconductordevices having electric connection contacts on their surfaces, mutuallyseparating the semiconductor devices in a surface region of thesemiconductor substrate, coupling the electric connection contacts tothe conductor pattern, and subsequently separating the semiconductordevices from the semiconductor substrate.
 2. A method as claimed inclaim 1, wherein at least a part of the electric connection contacts isconnected to the conductor pattern in an electrically conducting manner.3. A method of manufacturing a display device, in which a substrate isprovided with groups of at least one pixel and in which a semiconductordevice for supplying drive voltages to the pixel is fixed to thesubstrate, the method comprising the steps of providing a semiconductorsubstrate with a plurality of semiconductor devices having electricconnection contacts on their surfaces, mutually separating thesemiconductor devices in a surface region of the semiconductorsubstrate, subsequently separating the semiconductor devices from thesemiconductor substrate, and subsequently providing the substrate with aconductor pattern at least at the location of the semiconductor devicesand coupling the electric connection contacts to the conductor pattern.4. A method as claimed in claim 3, wherein at least a part of theelectric connection contacts is connected to the conductor pattern in anelectrically conducting manner.
 5. A method as claimed in claim 1 or 3,wherein the semiconductor devices have the same pitch as the groups ofpixels in at least one dimension.
 6. A method as claimed in claim 1 or3, wherein a semiconductor device is associated with a plurality ofpixels.
 7. A method as claimed in claim 6, wherein the semiconductordevice comprises drive electronics for the pixels.
 8. A method asclaimed in claim 1 or 3, wherein the semiconductor devices are separatedby means of an etching treatment in a surface region of thesemiconductor substrate.
 9. A method as claimed in claim 1 or 3, whereinthe semiconductor devices are provided in a semiconductor layer on aninsulating layer (19) and are separated by means of an etchingtreatment.
 10. A method as claimed in claim 1 or 3, wherein thesubstrate is flexible.
 11. A method of manufacturing an electronicdevice, in which at least a substrate is provided with functional groupscomprising at least a switching element, and in which a semiconductordevice for supplying drive voltages to the switching element is fixed tothe substrate, the method comprising the steps of providing thesubstrate with a conductor pattern, providing a semiconductor substratewith a plurality of semiconductor devices having electric connectioncontacts on their surfaces, mutually separating the semiconductordevices in a surface region of the semiconductor substrate, coupling theelectric connection contacts to the conductor pattern, and subsequentlyseparating the semiconductor devices from the semiconductor substrate.12. A method as claimed in claim 11, wherein at least a part of theelectric connection contacts is connected to the conductor pattern in anelectrically conducting manner.
 13. A method of manufacturing anelectronic device, in which at least a substrate is provided withfunctional groups comprising at least a switching element, and in whicha semiconductor device for supplying drive voltages to the switchingelement is fixed to the substrate, the method comprising the steps ofproviding a semiconductor substrate with a plurality of semiconductordevices having electric connection contacts on their surfaces, mutuallyseparating the semiconductor devices in a surface region of thesemiconductor substrate, subsequently separating the semiconductordevices from the semiconductor substrate, and providing the substratewith a conductor pattern and coupling the electric connection contactsto the conductor pattern.
 14. A method as claimed in claim 13, whereinat least a part of the electric connection contacts is connected to theconductor pattern in an electrically conducting manner.
 15. A method asclaimed in claim 11 or 13, wherein the semiconductor devices have thesame pitch as the functional groups in at least one dimension.